Commander Keen is an episodic video game developed by id Software in the early 1990s. The series focuses on the adventures of Billy Blaze, an 8-year-old boy who travels through space and assumes the secret identity of "Commander Keen". The series was successful at replicating the side-scrolling action of the Nintendo Entertainment System Super Mario Bros. games in DOS. The cartoon-style platform games are notable for their pioneering use of EGA graphics and shareware distribution, and they were some of the first games by id Software (who went on to later develop Wolfenstein 3D, Doom and Quake). The games were also exciting to the PC gaming community of the time because of John D. Carmack's smooth-scrolling graphics game engine, which first allowed smooth side scrollers on PC by only redrawing the elements of the screen that actually changed frame to frame.

Today is Commander Keen's 25th birthday. Keen was one of the very first games I ever played, and everybody I knew at the time was into Keen as well. We swapped floppies around with Keen on them, and I must've finished many of the episodes countless times. Commander Keen is part of my childhood, and a landmark in (PC) gaming.

In honour of Keen's 25th birthday, John Romero published a video today, in which he shows id Software's "port" (reverse engineering is probably more accurate) of Super Mario Bros. 3 to the PC. It was created without Nintendo's consent, and then sent to Nintendo for evaluation. The company had no interest in it, but the knowledge gained would come to use for Keen.